Li Z, Yu A, Weiner A M
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520-8114, USA.
J Virol. 1998 May;72(5):4183-91. doi: 10.1128/JVI.72.5.4183-4191.1998.
Adenovirus type 12 (Ad12) infection of human cells induces four chromosomal fragile sites corresponding to the U1 small nuclear RNA (snRNA) genes (the RNU1 locus), the U2 snRNA genes (RNU2), the U1 snRNA pseudogenes (PSU1), and the 5S rRNA genes (RN5S). Ad12-induced fragility of the RNU2 locus requires U2 snRNA transcriptional regulatory elements and viral early functions but not viral replication or integration, or chromosomal sequences flanking the RNU2 locus. We now show that Ad12 cannot induce the RNU1, RNU2, or PSU1 fragile sites in Saos-2 cells lacking the p53 and retinoblastoma (Rb) proteins but that viral induction of fragility is rescued in these cells when the expression of wild-type p53 or selected hot-spot mutants (i.e., V143A, R175H, R248W, and R273H) is restored by transient expression or stable retroviral transduction. We also observed weak constitutive fragility of the RNU1 and RNU2 loci in cells belonging to xeroderma pigmentosum complementation groups B and D (XPB and XPD) which are partially defective in the ERCC2 (XPD) and ERCC3 (XPB) helicase activities shared between the repairosome and the RNA polymerase H basal transcription factor TFIIH. We propose a model for Ad12-induced chromosome fragility in which interaction of p53 with the Ad12 E1B 55-kDa transforming protein (and possibly E4orf6) induces a p53 gain of function which ultimately perturbs the RNA polymerase II basal transcription apparatus. The p53 gain of function could interfere with chromatin condensation either by blocking mitotic shutdown of U1 and U2 snRNA transcription or by phenocopying global or local DNA damage. Specific fragilization of the RNU1, RNU2, and PSU1 loci could reflect the unusually high local concentration of strong transcription units or the specialized nature of the U1 and U2 snRNA transcription apparatus.
12型腺病毒（Ad12）感染人类细胞会诱导出四个与U1小核RNA（snRNA）基因（RNU1位点）、U2 snRNA基因（RNU2）、U1 snRNA假基因（PSU1）和5S rRNA基因（RN5S）相对应的染色体脆弱位点。Ad12诱导的RNU2位点脆弱性需要U2 snRNA转录调控元件和病毒早期功能，但不需要病毒复制或整合，也不需要RNU2位点侧翼的染色体序列。我们现在表明，在缺乏p53和视网膜母细胞瘤（Rb）蛋白的Saos-2细胞中，Ad12不能诱导RNU1、RNU2或PSU1脆弱位点，但当通过瞬时表达或稳定的逆转录病毒转导恢复野生型p53或选定的热点突变体（即V143A、R175H、R248W和R273H）的表达时，这些细胞中病毒诱导的脆弱性得以挽救。我们还观察到，属于着色性干皮病互补组B和D（XPB和XPD）的细胞中，RNU1和RNU2位点存在微弱的组成性脆弱性，这些细胞在修复体和RNA聚合酶H基础转录因子TFIIH共有的ERCC2（XPD）和ERCC3（XPB）解旋酶活性方面存在部分缺陷。我们提出了一个Ad12诱导染色体脆弱性的模型，其中p53与Ad12 E1B 55 kDa转化蛋白（可能还有E4orf6）的相互作用诱导p53功能获得，最终扰乱RNA聚合酶II基础转录装置。p53功能获得可能通过阻断U1和U2 snRNA转录的有丝分裂关闭或通过模拟全局或局部DNA损伤来干扰染色质凝聚。RNU1、RNU2和PSU1位点的特异性脆弱化可能反映了强转录单元异常高的局部浓度或U1和U2 snRNA转录装置的特殊性质。
